This invention relates to hydrocarbon conversion catalysts, and particularly to those utilized to catalyze the reaction of hydrogen with organic compounds containing nitrogen and/or sulfur so as to yield a denitrogenated and/or desulfurized product. More particularly, the invention is directed to catalysts and a method for preparing catalysts useful for the hydrodenitrogenation and/or hydrodesulfurization of hydrocarbon liquids. The invention is especially directed to catalysts of high hydrodenitrogenation activity.
In the refining of liquid hydrocarbons derived from mineral oils and other sources, it is often desirable to subject the liquid hydrocarbon or fraction thereof to hydrotreating. Hydrotreating is a refining process wherein liquid hydrocarbons are reacted with hydrogen. Hydrotreating is often employed to reduce the hydrocarbon concentration of olefins and oxygen. Hydrotreating is most commonly employed, however, to reduce the hydrocarbon concentration of nitrogen and/or sulfur. Reducing the concentration of nitrogen and sulfur produces a product hydrocarbon which, when eventually combusted, results in reduced air pollutants of the forms NO.sub.x and SO.sub.x. Reducing the concentration of nitrogen is also desirable to protect other refining processes, such as hydrocracking, which employ catalysts which deactivate in the presence of nitrogen.
In general, the hydrotreating of a nitrogen and/or sulfur-containing feedstock is carried out by contacting the feedstock with hydrogen at elevated temperatures and pressures and in the presence of a suitable catalyst so as to convert the nitrogen to ammonia and the sulfur to hydrogen sulfide.
A typical hydrotreating catalyst comprises particles containing a Group VIII active metal component and a Group VIB active metal component supported on a refractory oxide such as alumina. Phosphorus components are commonly incorporated into the catalyst to improve its activity by increasing its acidity. One catalyst which has been successfully employed on a commercial basis consists essentially of molybdenum, nickel, and phosphorus components supported on gamma alumina. A typical preparation procedure for such a catalyst is as follows: particles of hydrated alumina are firstly formed into a desired size and shape by extruding the hydrated alumina through a die having circular or polylobal-shaped openings therein and cutting the extruded matter into particles (or extrudates) of 1/16 to 1/2-inch lengths. The extrudates are calcined at temperatures between about 1,150.degree. and about 1,250.degree. F., whereby the extrudate composition is transformed into gamma alumina. The extrudates are then contacted with an impregnating solution comprising dissolved salts of molybdenum and nickel in aqueous phosphoric acid, and the impregnated extrudates (or composites) are subjected to a second calcination at temperatures typically between about 850.degree. F. and 1,100.degree. F. This second calcination converts the impregnated metals to their oxide forms. The metal oxides are then converted to sulfides, typically by contact at elevated temperatures with a hydrogen-hydrogen sulfide mixture or by contact with hydrogen and a hydrocarbon liquid containing organic sulfur compounds. Because of the problems inherent in the storage and transportation of sulfided catalyst, this final sulfiding step is usually carried out, not by the catalyst manufacturer, but by the catalyst user. Thus, the user normally purchases the catalyst in its oxide form, loads the catalyst into a hydrotreating reactor, and therein converts the catalyst metals to sulfides, either by contacting the catalyst with a specially prepared sulfiding mixture or by simply contacting the catalyst with hydrogen and an organic sulfur-containing feedstock. The resultant composition is a catalyst of high activity for simultaneous hydrodenitrogenation and hydrodesulfurization under conventional hydrotreating conditions.
Despite the high hydrodenitrogenation and hydrodesulfurization activity of the catalysts of the prior art, catalysts of yet higher activities are still being sought. The higher the activity of the catalyst, the lower the hydrotreating reactor temperature required to obtain a product of given nitrogen and sulfur content from a given feedstock. The lower the reactor temperature, the lower the expense of hydrotreating a given unit of feedstock due to the savings in process heat requirements, and the longer the onstream life of the catalyst due to the lower rate of coke formation.
Accordingly, it is a major object of this invention to provide a catalyst with superior hydrodenitrogenation activity and to provide a method for utilizing such a catalyst to achieve superior hydrodenitrogenation results.
It is a further object of this invention to provide a catalyst with superior hydrodesulfurization activity and to provide a method for utilizing such a catalyst to achieve superior hydrodesulfurization results.
It is a further object of this invention to provide a hydrodenitrogenation and hydrodesulfurization catalyst which can be used to denitrogenate or desulfurize a given feedstock for a longer continuous period of time.
It is a still further object of this invention to provide a method for preparing a catalyst with superior hydrodenitrogenation and desulfurization activity.
These and other objects and advantages of this invention will become apparent to those skilled in the relevant art in view of the following description of the invention.